Photovoltaic (PV) panels (here also referred to as solar panels) use radiant light from the sun to produce electrical energy. The solar panels include a number of PV cells to convert the sunlight into the electrical energy. The majority of solar panels use wafer-based crystalline silicon cells or a thin-film cell based on cadmium telluride or silicon. Crystalline silicon, which is commonly used in the wafer form in PV cells, is derived from silicon, a commonly used semi-conductor. PV cells are semiconductor devices that convert light directly into energy. When light shines on a PV cell, a voltage develops across the cell, and when connected to a load, a current flows through the cell. The voltage and current vary with several factors, including the physical size of the cell, the amount of light shining on the cell, the temperature of the cell, and external factors.
A solar panel (also referred to as PV module) is made of PV cells arranged in series and parallel. For example, the PV cells are first coupled in series within a group. Then, a number of the groups are coupled together in parallel. Likewise a PV array (also referred to as solar array) is made of solar panels arranged in series and in parallel. Two or more PV arrays located in physical proximity to each other are referred to as a PV array site.
The electrical power generated by each solar panel is determined by the solar panel's voltage and current. In a solar array electrical connections are made in series to achieve a desired output string voltage and/or in parallel to provide a desired amount of string current source capability. In some cases, each panel voltage is boosted or bucked with a DC-DC converter.
The solar array is connected to an electrical load, an electrical grid or an electrical power storage device, such as, but not limited to, battery cells. The solar panels deliver Direct Current (DC) electrical power. When the electrical load, electrical grid or electrical power storage device operates using an Alternating Current (AC), (for example, sixty cycles per second or 60 Herz (Hz)), the solar array is connected to the electrical load, electrical grid, or electrical power storage device, through a DC-AC inverter
Solar panels exhibit voltage and current characteristics described by their I-V curve. When the solar cells are not connected to a load, the voltage across their terminals is their open circuit voltage, Voc. When the terminals are connected together to form a short circuit, a short circuit current, Isc, is generated. In both cases, since power is given by voltage multiplied by current, no power is generated. A Maximum Power Point (MPP) defines a point wherein the solar panels are operating at a maximum power.
In a conventional solar array, all of the individual panels in the array must receive full sunlight for the array to work properly. If a portion of the array is shaded or otherwise impaired, the entire array power output—even from those sections still exposed to sunlight—is lowered. Inevitably, efficiency reducing variations among panels exist in many solar arrays. A significant amount of energy is left unrealized when these variations go undetected and uncorrected.